To satisfy your curiosity, I was told this by a Nikon technician at their Hollywood Calif Service Center. The way to tell if an MB-D11 is genuine or a knockoff is to open the battery compartment.
The cast magnesium original from Nikon is smooth on the inside. The plastic imitations have reinforcing ribs to strengthen the grip.
I wasn't at Nikon because of my grip, but for a lens problem. But I had recently returned an Amazon import grip for the D7000. It was called a Pixel, and had electrical problems. I bought the real Nikon item from BH Photo and am quite pleased.